RGB Project Completed

[Anthony P]

I purchased the RGB "White Light Engine" from holokid. After about a month I finally have it running. The diodes are blue PLT5 450B, green PL 530, and red Ushio HL63603TG. All are individually driven by LM317 CC custom tailored to adjust current from threshold to manufacture rated max. The green also has a CV source for the heater.
The module arrived with the red diode DOA. I purchased a replacement from DTR. With great effort, I was able to press it into its mount and secure the mount with Arctic Silver. The dichroic mirrors were very poorly aligned and non-adjustable. I, therefore, adjusted them anyway with procedures to test the patience if Jobe. Using dental probes, micro-tweezers, and some carefully placed dabs of epoxy, I was able to bring alignment into an acceptable level.
Please do not interpret this as a boo-hoo bitch session. The entire purpose of this project was to gain knowledge and experience in order to design a "good" RGB project. I now know that I want kinematic mounts that are easy to work with. I also gained much driver insight. The new project will use 3 Blach Buck drivers, PLTB 450B, NDG7475,and mitsu 500mW, all from DTR. I will mount everything on a plate with TECs and thermostats.

Now for the best part... pictures!

https://imgur.com/a/QnsYkAS

 

[DTR]

Great work getting it back up and running. Looks great. Good luck on the new project.

 

[paul1598419]

Nice job, Tony. I remember when you got it. Glad you were able to replace the bad diode and get it aligned.

 

[Mandelvolt]

I also have one of these laser modules and plan to use it for holography. Do you have additional details regarding the driver unit you constructed? I'm hoping to get as stable of a power source as possible (vs the highest output power), although it seems like using some VRM's and a bench supply to construct a simple constant current source might be the cheapest/best option at the moment. Any constructive feedback?

 

[Anthony P]

I also have one of these laser modules and plan to use it for holography. Do you have additional details regarding the driver unit you constructed? I'm hoping to get as stable of a power source as possible (vs the highest output power), although it seems like using some VRM's and a bench supply to construct a simple constant current source might be the cheapest/best option at the moment. Any constructive feedback?

As I said in the beginning. Each diode is controlled by LM317 in CC mode. The green heater additionally has LM317 CV for about 2V +/- 0.25V. The meters are "off-the-shelf" current meters powered separate from the diodes they monitor. Their power comes straight from wall adapter before any regulators. They are in series with diode ground.
If you have specific questions, I will do my best to answer.

 

[Mandelvolt]

Thanks, I've taken a few EE classes and optical physics classes but that was about 10 years ago so I'm trying to get those wheels turning again... I totally skimmed over your LM317 CC current, everything I've read seems to suggest this is the way to go. Any advice to keep things stable to prevent mode hopping and increase temporal coherence for holography? I think running caps in parallel to the load is one way, although any pointers for stability are appreciated
When adding a heatsink, is the housing sufficient to just bolt it to a heatsink or did you have to add additional thermal compound between the laser diodes and the housing? Tempted to zip tie the laser module to an old CPU heatsink.

 

[paul1598419]

Use Arctic Alumina adhesive to mount your laser module to a heat sink. I wouldn't use it where you plan on removing it later, however. It holds very tightly. But, it is the preferred method for heat sinking smaller heat sinks to larger ones.

 

[Anthony P]

Just ran test. After 15 min, temp seems stable (about 6 degrees F over ambient). I have module clamped and greased to modest heat-sink (.5x1.5x2.5" Al fins). All Lm317s are heat-sinked with tiny fan. Output power of power supply and diodes read stable.
CPU heat-sink sounds fine to me. I would not use fan due to vibration. I have heard that the laser itself can be mounted off of the optical bench and vibration from it will not affect holograms... I have never tired this. Also, I have never personally tested the coherence length of the red and blue diodes on interferometer, only the green.
It is common practice with pointer to overdrive the diodes. For this set up, I would stay conservative and within manufacturer specs for drive currents.
I used .1uF at each LM317 in, and 1uF at each out.
Hope this helps.

 

[paul1598419]

If you are planning on using this for full color holography, you will likely be disappointed. The green is the only laser with coherence length necessary for this.

 

[aaronnoraa]

If you are planning on using this for full color holography, you will likely be disappointed. The green is the only laser with coherence length necessary for this.

He would be better off replacing the red with Sharp's single mode GH0631IA2GC and the blue with a single mode Sharp GH04580A2G, perhaps then he may have a white light source usable for holography.

 

[paul1598419]

To increase the coherence length of direct diode lasers it would be better to diffraction tune these diodes and to keep them at a lower temperature than ambient.

 

[Mandelvolt]

Looks like I'll be replacing the red and blue lasers on this driver anyways. The laser diodes supplied by holokidd were junk, burned out within minutes even running conservatively and slightly below the recommended 165/150mA CC he posted on the "user guide". Driven at exactly 2.2V, the red one was bright for a few seconds before going dim and burning out, last reading on the power supply was 130mA...
*actually, this might be my power supply* blue laser flicked on for a second... Anyone else have ideas for making this work assuming the diodes are OK? I'm using a 5V CV/CC power supply.

 

[paul1598419]

If you are not using a driver for each laser that is your problem. Most here use a linear driver based on the LM317 IC. Laser diodes decrease in effective resistance as they heat up causing them to draw more current unless they are attached to a CC driver. There are lots of threads showing how to build one of these and they are very inexpensive to make.

 

[Anthony P]

Like Paul said, I used a separate LM317 CC driver for each diode... They did share main input power before drivers( 9v, 2A regulated wall adapter).

 

[Mandelvolt]

If you are not using a driver for each laser that is your problem. Most here use a linear driver based on the LM317 IC. Laser diodes decrease in effective resistance as they heat up causing them to draw more current unless they are attached to a CC driver. There are lots of threads showing how to build one of these and they are very inexpensive to make.

I'm using a CC/CV metered supply where you set the voltage and max current. I set it to about 2.2V w/ current limiting set to the max A indicated on the data sheet provided (160/80/130mA). Mostly it's because I'm afraid of going much above 2.4V for these modules and wanted to cap voltage and test before attaching to a 5V CC driver I have. Does anyone have experience running these at higher voltages or currents? I have a feeling I might be under-driving the diodes, although I assumed the mA given are for optimal operation.

 

[Anthony P]

I can send you the data sheets for each diode if you need them. 2.2v is not enough for the blue. Current must be controlled to be above threshold of the diode, but low enough to be safe range. Voltage, however, can be higher. I would try running the blue at 5-6v.
For that RGB, you essentially need 4 power supplies. I will open up my set up and post the readings later... gotta go to work now. Watch for edit in this post.